1. Field of the Invention
The present invention relates to a key input device for an input means of a device. More particularly, the present invention relates to a key input device for reducing the number of ports of a processor chip used for key recognition by equally dividing one of an inner terminal or an outer terminal of a switch board into a predetermined number and contacting them.
2. Description of the Related Art
In general, a number of electronic devices including portable terminals use a plurality of key button devices as a data input means. A conventional key button device includes an elastic pad with a plate shape, a plurality of key buttons disposed on the top surface of the elastic pad and having corresponding engraved characters and numbers thereon, and a plurality of protrusions (or actuators) disposed on the bottom surface of the elastic pad. Furthermore, a plurality of Light Emitting Devices (LEDs) for backlighting is included to obtain visibility of the key button device.
FIG. 1 is a sectional view of a conventional key pad assembly according to the related art. The key pad assembly 100 includes a key pad 110, a switch board 150, and a plurality of LEDs 170.
Referring to FIG. 1, the key pad 110 includes an elastic pad 120 formed of rubber and having a plate shape, a plurality of key buttons 140 disposed on the top surface 122 of the elastic pad 120 and having printed characters thereon, and a plurality of protrusions disposed on the bottom surface 124 of the elastic pad 120 opposite to the top surface 122. A corresponding protrusion is aligned on the middle of each of the key buttons 140. A plurality of grooves 126 may be formed in the bottom surface 124 of the elastic pad 120. The grooves 126 are disposed around each of the protrusions 130, thereby avoiding interference between the LEDs 170 and the protrusions 130.
The switch board 150 includes a Printed Circuit Board (PCB) 155 with a plate shape and a plurality of switches 160 disposed on the top surface of the PCB 155 opposite to the key pad 110. Each switch 160 consists of a conductive contact member 162 and a conductive dome sheet 164 covering the contact member 162 completely.
FIG. 2 is a view of a conventional switch board according to the related art. The switch board consists of an inner terminal 210 and a single outer terminal 220 surrounding the inner terminal 210. The inner terminal 210 and the outer terminal 220 may be connected using a dome sheet. Each key input is accomplished by a combination of a column line 240 and a row line 230. The column line 240 is connected to the inner terminal 210, and the row line 230 is connected to the outer terminal 220. If a signal transmission process using key input is briefly examined, in the key pad assembly structure of FIG. 1, the key button 140 is pressed by a user and the switch 160 below the key button 140 is pressed by the protrusion 130, so that the inner terminal 210 and the outer terminal 220 are connected by the dome sheet constituting the switch 160.
At this point, current flows into a processor chip through the switch connection, and the processor chip detects this flowing current to recognize the input by the user provided through the key button 140. On the contrary, if the switch 160 is disconnected, the inner terminal 210 and the outer terminal 220 are disconnected so that current no longer flows into the processor chip. That is, the key input is detected by ON/OFF of the current inputted into the processor chip.
Referring to FIG. 2, the column line 240 and the row line 230, which are connected to the switch board, are arranged in a matrix and thus constitute each key button input port. That is, in order to realize twelve (3×4) key buttons, the processor chip requires seven pins. If the number of key buttons to be realized is increased, the number of pins in a processor chip is increased in proportion to the number of key buttons.
Accordingly, in order to realize an input device with a number of key buttons such as a Qwerty key, since the number of pins for key input detection is increased in proportion to the number of realized key buttons in a processor chip, a size of the processor chip is increased. As a result, a size of a portable terminal is increased.
Therefore, a need exists for a system and method for providing a key input device that contributes to the miniaturization of a chip, by connecting key buttons with the minimum port and reducing an input/output signal line, to ultimately miniaturize a portable terminal and possibly reduce its manufacturing cost.